1. Field of the Invention
The present invention relates to an image heating apparatus that fixes or temporarily fixes an unfixed image formed and born on a recording material through a transfer system or a direction system as a permanent fixed image by heating, or heats an image on a recording material to improve the surface property such as gloss, and an image forming apparatus having the image heating apparatus.
2. Related Background Art
Up to now, many of copying machines, printers and the like using, for example, the electrophotographic system adopt a device of a contact heating type heat roller fixing system which is excellent in safety and an energy saving type film heating system as a heat fixing device (fixing unit) which is the image heating apparatus.
The heat fixing device of the heat roller fixing system i s basically made up of a heat roller (fixing roller) as a heating rotary member and an elastic pressure roller as a pressure rotary member, which is in press contact with the heat roller. The paired rollers are rotated to introduce a recording material (a transfer material sheet, an electrostatic recording paper, an electro fax paper, a printing sheet, etc.) as a heating material on which an unfixed image (hereinafter referred to as xe2x80x9ctoner imagexe2x80x9d) is formed and borne into a fixing nip portion which is a pressure contact nip portion of the paired rollers and to convey the recording material through the fixing nip portion while nipping the recording material at the fixing nip portion, thereby fixing a toner image on a recording material surface due to a heat from the heating roller and the pressure force of the fixing nip portion as a permanently fixed image.
Also, the heat fixing device of the film heating system has been proposed in, for example, Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open Nos. 2-157878, 4-44075 to 4-44083, 4-204980 to 4-204984, and so on. In the device, a heat resistant film (fixing film) which is a heating rotary member is conveyed while it is brought in close contact with a heating member such as a ceramic heater which is fixed by the heating rotary member (elastic pressure roller), and the recording material that bears the toner image is introduced into the fixing nip portion which is a pressure contact nip portion formed by the heating member and the pressure rotary member with the film interposed therebetween and then conveyed together with the film, to thereby fix the toner image on the recording material as a permanent image due to the heat given from the heating member through the film and the pressure force of the fixing nip portion.
The heat fixing device of the film heating system can save an electric power and reduce a wait time (quick start) because a low heating capacity linear heating member such as a ceramic heater can be used as a thin film of a low heating capacity. Also, in the heat fixing device of the film heating system, there have been known, as a film driving method, a method in which a driving roller is disposed on an inner surface of the film, and a method in which the pressure roller is used as the driving roller and the film is driven due to a frictional force between the driving roller and the pressure roller. In recent years, there are frequently employed the pressure roller driving system which is small in the number of parts and low in the costs.
In the above heat fixing device, there has been known that the fixing property of the toner image on the recording material largely depends on the thickness and the surface property of the recording material. In particular, a paper of the type having the rough surface property is remarkably low in the fixing property. This is because the sufficient quantity of heat is not supplied to toner on the recording material since a contact area between the heating member and recording material is reduced within the fixing nip portion.
As a result, to obtain an excellent fixing property even in the paper of the type having the inferior surface property, it is necessary to raise the fixing pressure force or raise the fixing temperature.
However, the method of making the fixing pressure rise is liable to increase the costs of the device because the drive torque of the heat fixing device becomes high. In particular, in the heat fixing device of the film heating system, because the film which is the heating rotary member is slid with respect to the heating member serving as a heat source at the fixing nip portion, thereby being liable to increase the rotary torque, it is difficult to increase the pressure force, and the limit of the total pressure is about 15 kg, and the linear pressure within the fixing nip region is comparatively low. For that reason, in order to improve the fixing property of a paper of the type which is low in the surface property, the fixing temperature must be made to rise.
However, in the case where the fixing temperature is only made high, the excessive quantity of heat is supplied to a thin paper or a paper excellent in the surface property, resulting in such problems that hot offset occurs or the curl degree of the paper becomes large.
Also, in the heat fixing device of the film heating system of the pressure roller driving type, there frequently occurs such a phenomenon that when a thin film high in smoothness passes, in the case where the film absorbs moisture, fixing operation is conducted at the high fixing temperature, a large amount of steam occurs, a steam layer is produced between the pressure roller and the paper, the coefficient of friction of the pressure roller is extremely lowered, a paper conveying force disappears and the paper slips, whereby the paper stops within the fixing nip.
Also, not only the fixing temperature but also the fixing nip width is an important parameter with respect to the adverse phenomenon such as the fixing property of the toner image on the recording material, the curl of the recording material, the hot offset of toner or the slip of the recording material.
In other words, if the fixing nip width is large, even if the fixing temperature is low, the quantity of heat is liable to move to the recording material, thereby being capable of exhibiting the excellent fixing property. Conversely, the phenomenon such as curl, hot offset or slip is liable to occur. The fixing nip width mainly depends on the hardness of the pressure roller and the pressure force of the pressure spring, and the hardness and the pressure force vary to some degree, and the fixing nip width is different in each of the heat fixing devices. For that reason, if the fixing temperature is set taking the variation of the fixing nip width into consideration, it is very difficult to satisfy all of the phenomenon such as the fixing property, curl, hot offset or slip with respect to various papers by only one kind of temperature setting as described above.
In this way, it is difficult to satisfy the optimum fixing conditions for both of the paper of the type rough in the surface property and the paper of the type excellent in the smoothness, and up to now, a user copes with this difficulty by selecting the fixing temperature setting in accordance with the kind of paper. However, it is difficult to set the fixing mode by the parameter which is hardly understood by a user, and therefore it is desirable to automatically set the optimum fixing temperature in accordance with the kind of paper (in particular, the roughness of the surface).
An object of the present invention is to provide an image heating apparatus and an image forming apparatus having the image heating apparatus which are capable of solving the above technical problems.
In order to achieve the above object, according to the present invention, there is provided an image heating apparatus, comprising:
temperature detecting means for detecting a temperature of a heating member or a heating rotary member;
current control means for controlling current to the heating member so that the temperature detected by the temperature detecting means reaches a target temperature;
power monitoring means for monitoring an electric energy supplied to the heating member, and
correcting means for correcting the target temperature on the basis of the monitor result by the power monitoring means.
Preferably, the image heating apparatus further comprises a heating rotary member sliding on an inner surface of the heating member; and
a pressure rotary member that forms a nip portion in association with the heating member through the heating rotary member;
characterized in that a recording material that bears an image is nipped and conveyed between the heating rotary member and the pressure rotary member to heat the image on the recording material due to a heat from the heating member through the heating rotary member.
Preferably, the correcting means includes detecting means for detecting the thickness of a transfer material and corrects the target temperature in accordance with the detected thickness.
Preferably, the image heating apparatus further comprises means for setting the target temperature in accordance with the number of continuously passing sheets and intervals of passing sheets or an operation mode set by an operator.
Preferably, the heating rotary member comprises a flexible thin endless film which is 20 to 150 xcexcm in thickness and has a mold release layer formed on the surface thereof.
Preferably, the power monitoring means monitors the electric energy supplied to the heating member when a leading portion of the recording material is heated.
Preferably, the power monitoring means monitors the electric energy supplied to the heating member in a state where a detected temperature is maintained to about the target temperature.
Preferably, the current control means controls the current to the heating member by a phase angle or wave number so that the temperature detected by the temperature detecting means becomes the target temperature.
According to the present invention, there is provided an image forming apparatus including image forming means for forming an image on a recording material; a heating rotary member which slides while an inner surface of the heating rotary member is in contact with the heating member; and a pressure rotary member that forms a nip portion in association with the heating member through the heating rotary member; in which a recording material that bears an image is nipped and conveyed between the heating rotary member and the pressure rotary member to fix the image on the recording material due to a heat from the heating member through the heating rotary member, the image forming apparatus comprising:
temperature detecting means for detecting a temperature of a heating member or a heating rotary member;
current control means for controlling current to the heating member so that the temperature detected by the temperature detecting means reaches a target temperature;
power monitoring means for monitoring an electric energy supplied to the heating member; and
correcting means for correcting the target temperature on the basis of the monitor result by the power monitoring means.
Preferably, the correcting means includes detecting means for detecting the thickness of the recording material and corrects the target temperature in accordance with the detected thickness.
Also, according to the present invention, there is provided an image heating apparatus, comprising:
temperature detecting means for detecting a temperature of a heating member or a heating rotary member; and
current control means for controlling the current to the heating member;
characterized in that the current control means has a first current control mode that controls the current to the heating member so that a constant power is supplied to the heating member if the temperature detected by the temperature detecting means is within a given range.
Preferably, the image heating apparatus further comprises a heating rotary member which slides while an inner surface of the heating rotary member is in contact with the heating member; and a pressure rotary member that forms a nip portion in association with the heating member through the heating rotary member; characterized in that a recording material that bears an image is nipped and conveyed between the heating rotary member and the pressure rotary member to heat the image on the recording material due to a heat from the heating member through the heating rotary member.
Preferably, the image heating means includes detecting means for detecting the thickness of the recording material and the current control means controls the current to the heating member in accordance with the detected thickness.
Preferably, the current control means has a second current control mode that controls the current to the heating member so that the temperature detected by the temperature detecting means becomes the target temperature.
Preferably, the image heating apparatus further comprises means for setting the target temperature in accordance with the number of continuously passing sheets and intervals of passing sheets or an operation mode set by an operator.
Preferably, the current control means controls the current to the heating member by a phase angle or wave number.
Preferably, the current control means controls the current to the heating member by changing over from the first current control mode to the second current control mode if the temperature detected by the temperature detecting means in the first current control mode becomes out of the given range.
Preferably, the heating rotary member comprises a flexible thin endless film which is 20 to 150 xcexcm in thickness and has a mold release layer formed on the surface thereof.
According to the present invention, there is provided an image forming apparatus including image forming means for forming an image on a recording material; a heating rotary member which slides while an inner surface of the heating rotary member is in contact with the heating member; and a pressure rotary member that forms a nip portion in association with the heating member through the heating rotary member; in which a recording material that bears an image is nipped and conveyed between the heating rotary member and the pressure rotary member to fix the image on the recording material due to a heat from the heating member through the heating rotary member, the image forming apparatus comprising:
temperature detecting means for detecting a temperature of a heating member or a heating rotary member; and
current control means for controlling current to the heating member;
characterized in that the current control means has a first current control mode that controls the current to the heating member so that a constant power is supplied to the heating member if the temperature detected by the temperature detecting means is within a given range.
Preferably, the current control means further has a second current control mode that controls the current to the heating member so that the temperature detected by the temperature detecting means becomes the target temperature, and controls the current to the heating member by changing over from the first current control mode to the second current control mode if the temperature detected by the temperature detecting means in the first current control mode becomes out of the given range.
According to the present invention, because only a low power is supplied to a recording material of the type which is rough in the surface property if the heating temperature (fixing temperature) is the same, it is possible to automatically control an appropriate temperature in accordance with the surface roughness of the recording material through a method of automatically correcting the target temperature in accordance with the supply energy. As a result, the excellent image heating property (fixing property) can be obtained regardless of the surface property of the recording material.
Also, even in the case where the nip width is different in each of the image heating apparatuses, an apparatus wide in the nip width which makes it easy to supply the power to the recording material can correct the target temperature to a lower value whereas an apparatus narrow in the nip width which makes it difficult to supply the power to the recording material can correct the target temperature to a higher value, and the variation in the image heating property among the apparatuses can be suppressed to the minimum. As a result, a precision in the parts can be degraded to make it possible to reduce the costs of the apparatus.
Further, the optimum temperature can be set in accordance with the thickness of the recording material which is another parameter by which the supply power varies, to thereby making it possible to conduct the temperature control higher in precision.
In addition, even in a state where this control cannot follow a paper that greatly absorbs humidity, a recording material high in printing rate, an extremely thick paper or the like, the image heating property of the level that can be sufficiently satisfied can be obtained.
Preferably, a plurality of target temperature settings can be made by user""s setting. As a result, it is possible to provide an image heating apparatus having an appropriate image heating property in accordance with the kind of paper not to be controlled and the environments.
Other further objects, features and advantages of the invention will appear more fully from the following description.